Among the electronic devices comprising at least a part based on material provided by organic chemistry, organic light emitting diodes (OLEDs) have a prominent position. Since the demonstration of efficient OLEDs by Tang et al. in 1987 (C. W. Tang et al., Appl. Phys. Lett. 51 (12), 913 (1987)), OLEDs developed from promising candidates to high-end commercial displays. An OLED comprises a sequence of thin layers substantially made of organic materials. The layers typically have a thickness in the range of 1 nm to 5 μm. The layers are usually formed either by means of vacuum deposition or from a solution, for example by means of spin coating or jet printing.
OLEDs emit light after the injection of charge carriers in the form of electrons from the cathode and in form of holes from the anode into organic layers arranged in between. The charge carrier injection is effected on the basis of an applied external voltage, the subsequent formation of excitons in a light emitting zone and the radiative recombination of those excitons. At least one of the electrodes is transparent or semitransparent, in the majority of cases in the form of a transparent oxide, such as indium tin oxide (ITO), or a thin metal layer.
Some phosphepine compounds are known in the scientific literature, e.g. formation of 11-phenylbenzo[b]dinaphtho-[2,1-d:1′,2′-f]phosphepine-11-oxide (CAS 597578-28-6) by an intramolecular substitution reaction was reported in Bull. Chem. Soc. Jpn., 76, 1233-1244 (2003).
It is an objective of the invention to overcome the drawbacks of the prior art and to find compounds which can improve the performance of organic electronic devices. Specifically, the sought compounds shall be successfully embedded in electrically doped semiconducting materials for use in electronic devices. The inventive semiconducting materials shall afford devices with better characteristics, especially with low voltage and higher efficiency, more specifically, OLEDs with higher power efficiency, even more specifically, OLEDs having satisfactory efficiency and long lifetime.